Droplet actuators are used to conduct a wide variety of droplet operations. A droplet actuator typically includes two substrates separated by a gap. The substrates include electrodes for conducting droplet operations. The space is typically filled with a filler fluid that is immiscible with the fluid that is to be manipulated on the droplet actuator. The formation and movement of droplets is controlled by electrodes for conducting a variety of droplet operations, such as droplet transport and droplet dispensing. Because there is a need to produce droplets having more accurate and/or precise volumes for both samples and reagents, there is a need for alternative approaches to metering droplets in a droplet actuator. There is also a need for improved approaches to loading droplet operations fluids, such as samples and/or reagents, into and removing such fluids from a droplet actuator.